Memory device with write data bus control

ABSTRACT

Apparatuses and methods for transmitting data between a plurality of chips are described. An example apparatus includes: a first chip, wherein the first chip includes a receiver that receives a data strobe signal and further generates an internal strobe signal responsive, at least in part, to the data strobe signal, the internal strobe signal including a first edge and a second edge following the first edge; a buffer circuit coupled to a set of input terminals and captures first data at the set of input terminals responsive, at least in part, to the first edge of the internal strobe signal and further captures second data at the set of input terminals responsive, at least in part, to the second edge of the internal strobe signal; a driver coupled between the buffer circuit and a set of data terminals and configured to be activated to provide the first and second data from the buffer circuit to the set of data terminals responsive, at least in part, to a control signal; and a width expanding circuit that provides the control signal responsive, at least in part, to the internal strobe signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.16/225,303, filed Dec. 19, 2018 and issued as U.S. Pat. No. 10,553,263Feb. 4, 2020, which is a divisional of U.S. patent application Ser. No.15/365,563, filed Nov. 30, 2016, U.S. Pat. No. 10,163,469 issued Dec.25, 2018. These applications and patents are incorporated by referenceherein in their entirety and for all purposes.

BACKGROUND

High data reliability, high speed of memory access, lower powerconsumption and reduced chip size are features that are demanded fromsemiconductor memory. In recent years, three-dimensional (3D) memorydevices have been introduced. Some 3D memory devices are formed bystacking chips vertically and interconnecting the chips using throughsubstrate vias (TSVs) between an interface (I/F) chip and core chips.FIG. 1 is a block diagram of an apparatus including a memory controller1 and a memory device 10. The memory device 10 may include an interfacechip 2 and a plurality of core chips 3 CC0-CC3. Benefits of the 3Dmemory devices include shorter interconnects which reduce circuit delaysand power consumption, a large number of vertical vias between layerswhich allow wide bandwidth buses between functional blocks in differentlayers, and a considerably smaller footprint. Thus, the 3D memorydevices contribute to higher memory access speed, lower powerconsumption and chip size reduction. Example 3D memory devices includeHybrid Memory Cube (HMC), High Bandwidth Memory (HBM), and a wide-I/Odynamic random access memory (DRAM).

In a 3D memory device as described, each chip, such as the interfacechip or each core chip, may include a first-in-first-out (FIFO) type ofbuffer for write data. The FIFO type of buffer may receive write dataresponsive to a write data strobe signal (WDQS) and may provide anoutput signal responsive to an output clock signal. Thus, in the 3Dmemory device, the write data may be transmitted via two FIFO type ofbuffers, one in the interface chip and the other in the correspondingcore chip. However, the FIFO type of buffers delays the output signalbecause of waiting for a timing of being output responsive to the outputclock signal. Furthermore, the FIFO type of buffer in the interface chipmay be redundant for being responsive to an output clock signal in theinterface chip, because another FIFO type of buffer in the core chipthat receives the write data from the interface chip provides the writedata responsive to an output clock signal in the core chip. Thus, thewrite data from the FIFO type of buffer in the core chip is eventuallyadjusted based on the output clock signal in the core chip.

For example, High Bandwidth Memory (HBM) is a type of memory including ahigh-performance DRAM interface and vertically stacked DRAM. A typicalHBM stack of four DRAM core chips contains two channels per chip, andeach of the two channels includes 128 bit I/Os. The typical HBM stackmay contain a total of eight input/output channels and a width of 1024bits in total. An interface (I/F) chip of the HBM provides an interfacewith the eight input/output channels, which function independently ofeach other. Thus, the above 3D memory device may be include asubstantially large number of data terminals (DQs) (e.g., 1024 DQs) inthe interface chip. Because the FIFO type of buffer is provided for eachdata terminal, the large number of the FIFO type buffers may cause alarger layout size, in addition to the delay to write data signalsprovided to the core chips.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus including a memory controllerand a memory device.

FIG. 2A is a schematic diagram of an interface (IF) chip and a core chipin a memory device, in accordance with an embodiment of the presentdisclosure.

FIG. 2B is a timing diagram of signals in the interface (IF) chip andthe core chip in the memory device of FIG. 2A, in accordance with anembodiment of the present disclosure.

FIG. 3A is a block diagram of an interface (IF) command circuit in theIF chip of FIG. 2A, in accordance with an embodiment of the presentdisclosure.

FIG. 3B is a timing diagram of signals in the IF command circuit of FIG.3A, in accordance with an embodiment of the present disclosure.

FIG. 3C is a block diagram of an interface (IF) latency shifter in theIF command circuit, in accordance with an embodiment of the presentdisclosure.

FIG. 4A is a block diagram of a width expander circuit in the IF chip ofFIG. 2A, in accordance with an embodiment of the present disclosure.

FIGS. 4B and 4C are timing diagrams of clock signals in the widthexpander circuit of FIG. 4A, in accordance with an embodiment of thepresent disclosure.

FIG. 5A is a block diagram of an interface (IF) write buffer circuit inthe IF chip of FIG. 2A, in accordance with an embodiment of the presentdisclosure.

FIG. 5B is a timing diagram of signals in the IF write buffer circuit ofFIG. 5A, in accordance with an embodiment of the present disclosure.

FIG. 6A is a block diagram of a core command circuit in the core chip ofFIG. 2A, in accordance with an embodiment of the present disclosure.

FIG. 6B is a block diagram of a core latency shifter in the core commandcircuit, in accordance with an embodiment of the present disclosure.

FIG. 6C is a timing diagram of signals in the core command circuit ofFIG. 6A, in accordance with an embodiment of the present disclosure.

FIG. 7A is a block diagram of a core write FIFO circuit in the core chipof FIG. 2A, in accordance with an embodiment of the present disclosure.

FIG. 7B is a timing diagram of signals in the core write FIFO circuit,in accordance with an embodiment of the present disclosure.

FIG. 7C is a block diagram of a pointer circuit in the core write FIFOcircuit, in accordance with an embodiment of the present disclosure.

FIG. 7D is a block diagram of a clock gate block in the core write FIFOcircuit, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Various embodiments of the present invention will be explained below indetail with reference to the accompanying drawings. The followingdetailed description refers to the accompanying drawings that show, byway of illustration, specific aspects and embodiments in which thepresent invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent invention. Other embodiments may be utilized, and structure,logical and electrical changes may be made without departing from thescope of the present invention. The various embodiments disclosed hereinare not necessary mutually exclusive, as some disclosed embodiments canbe combined with one or more other disclosed embodiments to form newembodiments.

FIG. 2A is a schematic diagram of an interface (IF) chip 2 and a corechip 3 in a memory device 10, in accordance with an embodiment of thepresent disclosure. FIG. 2B is a timing diagram of the interface (IF)chip 2 and the core chip 3 in the memory device 10 of FIG. 2A, inaccordance with an embodiment of the present disclosure. For example,the memory device 10 may be an HBM, an HMC, a Wide-IO DRAM, etc. Thememory device 10 may include the interface chip 2 and a plurality ofcore chips 3 stacked with each other. The memory device 2 may includeconductive vias (TSVs) 31, 32, 33, 34 (e.g., through substrateelectrodes or through silicon vias) which couple the interface chip 2and core chips 3 by penetrating the core chips 3 and coupling to a clockterminal 311, a command terminal 321, a data strobe terminal 331 and aset of data terminals 291 of the interface chip 2, respectively. Also,the interface chip 2 may include a set of TSVs at a core chip sidecoupled to an upper core chip, and the plurality of core chips 3 mayinclude the TSVs 31, 32, 33, 34 at a core chip side coupled to the uppercore chip instead of an interface chip side coupled to the interfacechip 2.

In the interface chip 2, an IF command circuit 20 may receive aninternal clock signal CLKINT through a buffer 21 that receivescomplementary clock signals CLKt and CLKc provided to the memory device10. The IF command circuit 20 may provide the internal clock signalCLKINT from a CLKTSV node thereof to the TSV 31 via the clock terminal311. The IF command circuit 20 may receive a command signal COM througha buffer 22. The IF command circuit 20 may provide the command signalCOM from a COMTSV node thereof to the TSV 32 via the command terminal321. Responsive to the command signal COM indicative of a command (e.g.,a write command WRT for executing a write operation) at Time “a” in FIG.2B, a write state signal WRTSTATE may be activated (e.g., from a logiclow level to a logic high level) at Time “c” in FIG. 2B. The write statesignal WRTSTATE may be provided to an enable node of a buffer 24 forwrite data and an enable node of a buffer 23, which may function as astrobe receiver, for an internal write data strobe signal WDQS. Thestrobe receiver 23 may receive active write data strobe signals WDQStand WDQSc to the memory device 10, with a delay. The delay may berepresented by a latency that is a number of cycles included in thedelay due to an address strobe command latency. For example, a delay fora column address strobe (CAS) for the writing operation (e.g., Time “g”in FIG. 2B) may be represented by a CAS write latency (CWL) from thewrite command WRT (e.g., Time “f” in FIG. 2B, that may correspond toTime “a”) on the command signal COM. The delay to for the write data ofthe buffer 23 to be activated (e.g., Time “b” in FIG. 2B) may berepresented as (CWL−1) cycles from the command signal COM (e.g., Time“a” in FIG. 2B) indicative of the write command. The buffer 23 mayprovide the internal write data strobe signal WDQS to a width expandercircuit 26 (e.g. from Time “d”), a clock input (InClk) node of an IFwrite buffer circuit 27 and to a clock input (InClk) node of a corewrite FIFO circuit 36 via the data strobe terminal 331 of the interfacechip 2 and the TSV 33 in the core chip 3, responsive to the active writestate signal WRTSTATE.

Responsive to the activated write state signal WRTSTATE, the buffer 24may provide write data WDQ from a data terminal DQ to a data input (DIN)node of the IF write buffer circuit 27. For example, the write data WDQhaving a preamble signal may be provided from the buffer 24 to the IFwrite buffer circuit 27, until a first pulse (i.e. a first half cycle)of the internal write data strobe signal WDQS. After the first pulse,with the column address strobe (CAS) write latency (CWL) from thecommand signal COM indicative of the write command (e.g., at Time “e”),the buffer 24 may provide a first write data (A) responsive to a firstpredetermined edge (e.g., a second rising edge of WDQSt or a secondfalling edge of WDQSc), a second write data (B) responsive to a secondpredetermined edge (e.g., a second falling edge of WDQSt or a secondrising edge of WDQSc), a third write data (C) responsive to a thirdpredetermined edge (e.g., a third rising edge of WDQSt or a thirdfalling edge of WDQSc), and a fourth write data (D) responsive to afourth predetermined edge (e.g., a third falling edge of WDQSt or athird rising edge of WDQSc). The IF write buffer circuit 27 may capturethe write data WDQ at the DIN node, responsive to the internal writedata strobe signal WDQS received at the InClk node, and may furtherprovide the write data WDQ to a buffer 29 from a data output (DOUT)node. The width expander circuit 26 may receive the internal write datastrobe signal WDQS and provide a write buffer enable IF signalWRTBUFENIF that is active (e.g., at a logic high level) to control anenable node of the buffer 29 for enabling the buffer 29, responsive tothe internal write data strobe signal WDQS.

The buffer 29 may function as a driver that is activated to provide aread/write bus TSV signal RWBSTSV to a set of data terminals 291responsive to the active WRTBUFENIF signal. The set of data terminals291 of the IF chip 2 may be coupled to a TSV 34 in the core chip 3. Theread/write bus TSV signal RWBSTSV may include data from the DOUT node ofthe IF write buffer circuit 27. For example, the buffer 29 may provide“don't care data (X)” associated with the preamble signal until the endof the first active cycle of the write buffer enable IF signalWRTBUFENIF. The buffer 29 may provide the first write data (A) and thesecond write data (B) responsive to the second active cycle of the writebuffer enable IF signal WRTBUFENIF. The buffer 29 may provide the thirdwrite data (C) and the fourth write data (D) responsive to the thirdactive cycle of the write buffer enable IF signal WRTBUFENIF. Thus, thebuffer 29 may provide the don't care data and the first to fourth datato the TSV 34. On the other hand, the buffer 29 may be set to a highimpedance state if the WRTBUFENIF signal is deactivated (e.g., at alogic low level).

In the core chip 3, a core command circuit 30 may receive the internalclock signal CLKINT from the IF command circuit 20 through the TSV 31.The core command circuit 30 may receive the command signal COM from theIF command circuit 20 through the TSV 32. The core command circuit 30may provide a write internal clock signal WRTCLKCORE responsive to thecommand signal COM indicative of a write command and the internal clocksignal CLKINT. The WRTCLKCORE signal may have the same cycle as theinternal clock signal CLKINT while being activated, with a delayequivalent to the CWL cycles relative to the command signal COMindicative of the write command for executing a write operation. Thecore command circuit 30 may provide an active write command enablesignal WRTCOM from a WRTEN node and a WRTBUFENCORE node, responsive tothe command signal COM indicative of the write command. The active writecommand enable signal WRTCOM signal on the WRTBUFENCORE node may beactivated with a delay equivalent to a (CWL+1) cycles relative to thecommand signal COM indicative of the write command. Thus, the corecommand circuit 30 may provide the active write command enable signalWRTCOM signal after a predetermined number of cycles (e.g., one cycle)of providing the active WRTCLKCORE signal, responsive to the commandsignal COM. For example, the predetermined number of cycles may bedetermined to cover preamble cycles of core data to be provided from theIF chip 2.

The TSV 34 may provide the core data from the IF chip 2, including thedon't care data (X) in the preamble cycle and the first to forth writedata (A to D), on the RWBSTSV signal to a data input (DIN) node 341 ofthe core write FIFO circuit 36, with a delay due to the TSV 34 relativeto the RWBSTSV signal, responsive to the RWBSTSV signal. The core writeFIFO circuit 36 may receive a write data strobe signal WRITCLKTSV thatmay have a delay relative to the internal write date strobe signal WDQSdue to the TSV 33 from the TSV 33 at the InClk node. The write datastrobe signal WRTCLKTSV may include a first pulse for the don't caredata (X) in a first cycle (e.g., the preamble cycle), a second pulse forthe first and second data (A and B) to be received in a second cycle,and a third pulse for the third and fourth data (C and D) to be receivedin a third cycle. The core write FIFO circuit 36 may receive theWRTCLKCORE signal, which is independent from the write data strobesignal WRTCLKTSV, at an OutClk node. Because the WRTCLKCORE signal maybe activated with the CWL delay, the core write FIFO circuit 36 mayprovide the don't care data and the first to fourth data received at theDIN node 341 to a buffer 38 from a data output (DOUT) node, responsiveto the WRTCLKCORE signal. For example, the buffer 38 may be a tri-statebuffer. The buffer 38 may provide a signal from the DOUT node of thecore write FIFO circuit 36 as a read/write bus core signal RWBSCOREthroughout a core read/write bus through one or more core chips,responsive to the active WRTBUFENCORE signal. Because the WRTBUFENCOREsignal has the delay equivalent to the CWL+1 cycles relative to thecommand signal COM, whereas the WRTCLKCORE signal has the delay of CWLcycles, the don't care data in the first cycle of the signal from theDOUT node may not be provided by the buffer 38, and the first data tofourth data (A to D) maybe provided as the read/write bus core signalRWBSCORE.

FIG. 3A is a block diagram of an interface (IF) command circuit 20 inthe IF chip 2 of FIG. 2A, in accordance with an embodiment of thepresent disclosure. The IF command circuit 20 may receive the internalclock signal CLKINT at a CLK node and may further provide the internalclock signal CLKINT to the CLKTSV node. The IF command circuit 20 mayreceive the command signal COM at a COM node and may further provide thecommand signal COM to the COMTSV node.

The IF command circuit 20 may include a command decoder 201. The commanddecoder 201 may receive the command signal COM from the COM node of theIF command circuit 20. The command decoder 201 may decode the commandsignal COM to obtain a command. If the command is indicative of thewrite command for executing the write operation, the command decoder 201may provide an IF write command signal WRTCMIF that is active (e.g., ata logic high level).

FIG. 3B is a timing diagram of signals in the IF command circuit 20 ofFIG. 3A, in accordance with an embodiment of the present disclosure.FIG. 3C is a block diagram of an interface (IF) latency shifter 202 inthe IF command circuit 20, in accordance with an embodiment of thepresent disclosure. The IF latency shifter 202 may provide an activewrite state signal WRTSTATE at an OR node. The active write state signalWRTSTATE may have an active period for a predetermined latency,responsive to the active WRTCMIF signal and further responsive to theinternal clock signal CLKINT. For example, the predetermined latency maybe a column address strobe (CAS) write latency (CWL) (e.g., from Time“c” to Time “d” in FIG. 3B) plus one clock cycle, which is (CWL+1)cycles (e.g., from Time “c” to Time “e” in FIG. 3B). For example, the IFlatency shifter 202 may be a shift register which includes a pluralityof flip-flop circuits 203 in a cascade connection. The write commandsignal WRTCOM is provided to an input node of a flip-flop circuit FF1that is in a first stage of the plurality of flip-flop circuits 203 inthe cascade connection. Each flip flop circuit of the plurality offlip-flop circuits 203 may receive the internal clock signal CLKINT at aclock node. An output node of each flip flop circuit of the plurality offlip-flop circuits 203 may be coupled to an input node of a flip flopcircuit in a next stage of the plurality of flip-flop circuits 203 inthe cascade connection. The IF latency shifter 202 may include an ORcircuit 204 which may have a plurality of input nodes coupled to aplurality of corresponding output nodes of the plurality of flip-flopcircuits 203. Since the plurality of flip-flop circuits 203 may operatein synchronization with the internal clock signal CLKINT, the OR circuit204 may provide the write state signal WRTSTATE, which is a result of alogical OR operation of signals on the plurality of input nodes, to theOR node of the IF latency shifter 202. For example, the write statesignal WRTSTATE may have an active period for (CWL+1) cycles. The number“CWL+1” of the flip flop circuits 203 corresponds to a period of (CWL+1)cycles that is the latency represented by the write state signalWRTSTATE in the active state. The write state signal WRTSTATE may beprovided to the enable node of the buffer 23 for the internal write datastrobe signal WDQS and the enable node of the buffer 24 for write datain FIG. 2A.

FIG. 4A is a block diagram of a width expander circuit 26 in the IF chip2 of FIG. 2A, in accordance with an embodiment of the presentdisclosure. The width expander circuit 26 may receive the internal writedata strobe signal WDQS at a CLKIN node and provide the write bufferenable IF signal WRTBUFENIF that is active (e.g., at a logic high level)at a CLKOUT node, to the enable node of the buffer 29 in order tocontrol enabling/disabling the buffer 29. For example, the widthexpander circuit 26 may include one or more delay circuits 40 that causea delay that corresponds to an additional pulse width after expansion tothe internal write data strobe signal WDQS to be added, and provide thewrite buffer enable IF signal WRTBUFENIF having an active pulse widththat is longer than an active pulse width of the internal write datastrobe signal WDQS. FIGS. 4B and 4C are timing diagrams of clock signalsin the width expander circuit 26 of FIG. 4A, in accordance with anembodiment of the present disclosure. FIG. 4B includes a timing chart ofone cycle of the internal write data strobe signal WDQS at the CLKINnode and the write buffer enable IF signal WRTBUFENIF at the CLKOUT nodewhile a clock frequency of the internal write data strobe signal WDQS islow. As shown in FIG. 4B, a pulse width after the expansion with thedelay may not cover a whole cycle, if the clock frequency is low. FIG.4C includes a timing chart of one cycle of the internal write datastrobe signal WDQS at the CLKIN node and the write buffer enable IFsignal WRTBUFENIF at the CLKOUT node while the clock frequency of theinternal write data strobe signal WDQS is high. The pulse width afterthe expansion with the same delay may cover almost an entire cycle, ifthe clock frequency is high and the clock cycle is short, as shown inFIG. 4C. In order to provide the write buffer enable IF signalWRTBUFENIF to ensure all the write data (A, B, C, D) to be transmitted,it may be preferable to cover almost the entire cycle. The delay may notbe designed to exceed the clock cycle.

FIG. 5A is a block diagram of an interface (IF) write buffer circuit 27in the IF chip 2 of FIG. 2A, in accordance with an embodiment of thepresent disclosure. FIG. 5B is a timing diagram of signals in the IFwrite buffer circuit 27 of FIG. 5A, in accordance with an embodiment ofthe present disclosure. For example, the command signal COM may includetwo consecutive write commands WRT. The write data signal WDQ mayinclude write data (A and B) and the internal write data strobe signalWDQS may include two cycles corresponding to a preamble signal followedby two bytes to be transmitted in one cycle. The IF write buffer circuit27 may receive the write data signal WDQ at the DIN node, responsive tothe internal write data strobe signal WDQS received at the InClk node,and may further provide the write data signal WDQ to the buffer 29 fromthe DOUT node. For example, the IF write buffer circuit 27 may include acouple of flip-flop circuits 51 and 52. The flip-flop circuit 51 mayreceive the internal write data strobe signal WDQS at a clock node. Theflip-flop circuit 51 may latch first data on the write data signal WDQat a data node, responsive to rising edges of the internal write datastrobe signal WDQS, and may provide the don't care data X followed bythe write data, such as A, on the WDQ signal at rising edges of theinternal write data strobe signal WDQS as a WR signal. The flip-flopcircuit 52 may receive an inverted signal of the internal write datastrobe signal WDQS at a clock node. The flip-flop circuit 52 may latchsecond data on the write data WDQ at a data node, responsive to risingedges of the inverted write data signal strobe signal that are fallingedges of the internal write data strobe signal WDQS, and may provide thedon't care data X followed by the write data, such as B, on the WDQsignal at falling edges of the internal write data strobe signal WDQS asa WF signal.

The IF write buffer circuit 27 may include a multiplexer 53. Themultiplexer 53 may receive the WR signal and the WF signal, and mayprovide the WR signal responsive to an active state (e.g., a logic highlevel) of the internal write data strobe signal WDQS received at theInClk node, and provide the WF signal responsive to an inactive state(e.g., a logic low level) of the internal write data strobe signal WDQSreceived at the InClk node. The multiplexer 53 may provide the don'tcare data X for the first cycle of the internal write data strobe signalWDQS. The multiplexer 53 may provide the write data A at an active stateof the second cycle and the write data B at an inactive state of thesecond cycle. Thus, the IF write buffer circuit 27 may provide the writedata A and B preceded by the don't care data X from the DOUT node. Thus,the IF write buffer circuit 27 may capture the write data A responsive,at least in part, to the rising edge of the internal write data strobesignal WDQS and further captures the write data B responsive, at leastin part, to the falling edge of the internal write data strobe signalWDQS.

FIG. 6A is a block diagram of a core command circuit 30 in the core chip3 of FIG. 2A, in accordance with an embodiment of the presentdisclosure. The core command circuit 30 may receive the internal clocksignal CLKINT at a CLK node. The core command circuit 30 may receive thecommand signal COM at a COM node. The core command circuit 30 mayinclude a command decoder 301. The command decoder 301 may receive thecommand signal COM from the COM node of the core command circuit 30. Thecommand decoder 301 may decode the command signal COM to obtain acommand. If the command is indicative of the write command for executingthe write operation, the command decoder 201 may provide a write commandcore signal WRTCMCR that is active (e.g., at a logic high level) to acore latency shifter 302.

FIG. 6B is a block diagram of the core latency shifter 302 in the corecommand circuit 30, in accordance with an embodiment of the presentdisclosure. FIG. 6C is a timing diagram of signals in the core commandcircuit 30 of FIG. 6A, in accordance with an embodiment of the presentdisclosure. In response to two consecutive write commands WRT includingin the command signal COM, as shown in FIG. 5C, the command decoder 301may provide the write command core signal WRTCMCR that has been activefor two cycles. The core latency shifter 302 may receive the writecommand core signal WRTCMCR, and the internal clock signal CLKINT at aCLK node. The core latency shifter 302 may provide one or more enablesignals associated with predetermined latencies, responsive to theactive WRTCMCR signal and further responsive to the internal clocksignal CLKINT. For example, the predetermined latencies may include acolumn address strobe (CAS) write latency (CWL) (e.g., from Time “j” toTime “k” in FIG. 6C) plus one clock cycle, which is (CWL+1) cycles(e.g., from Time “a” to Time “b” in FIG. 6C). For example, the corelatency shifter 302 may be a shift register which includes a pluralityof flip-flop circuits 307 in a cascade connection. The write commandsignal WRTCMCR is provided to an input node of a flip-flop circuit FF1that is in a first stage of the plurality of flip-flop circuits 307 inthe cascade connection. Each flip flop circuit of the plurality offlip-flop circuits 307 may receive the internal clock signal CLKINT at aclock node. An output node of each flip flop circuit of the plurality offlip-flop circuits 203 may be coupled to an input node of a flip flopcircuit in a next stage of the plurality of flip-flop circuits 307 inthe cascade connection. The core latency shifter 302 may include an ORcircuit 308 which may have a plurality of input nodes coupled to anoutput node of a flip-flop circuit FF(CWL−1) 307 in the “(CWL−1)-th”stage and an output node of a flip-flop circuit FFCWL 307 in the“(CWL)-th” stage, to receive a latency signal corresponding to (CWL−1)cycles and a latency signal corresponding to (CWL) cycles, respectively.Since the plurality of flip-flop circuits 307 may operate insynchronization with the internal clock signal CLKINT, the OR circuit308 may provide a latency sum signal (CWL−1+0) at a “CWL−1+0” node ofthe core latency shifter 302, which has an active period for threecycles (e.g., from Time “i” to an end of a cycle that starts from Time“e” in FIG. 6C) as a result of an OR operation of the latency signalcorresponding to (CWL−1) and the latency signal corresponding to (CWL)cycles. Because each output signal of the plurality of the flip-flopcircuits FF(CWL−1) (e.g., which is active from Time “i” to from Time “e”in FIG. 6C) and FFCWL 307 may have a pulse width (e.g., an activeperiod) of two cycles (e.g., from Time “d” to the end of a cycle thatstarts from Time “e” in FIG. 6C) where the active period of theflip-flop circuit FFCWL 307 has one cycle delay relative to the activeperiod of the flip-flop circuit FF(CWL−1) 307, the active periods may beoverlapped for one cycle. The number “CWL+1” of the flip flop circuits307 corresponds to (CWL+1) cycles and a flip-flop circuit FF(CWL+1) 307may provide an active write command enable signal WRTCOM from a CWL+1node representing a CWL plus one cycle (CWL+1) latency, having a pulsewidth of two cycles, responsive to the two consecutive write commandsWRT. The core command circuit 30 may provide the active write commandenable signal WRTCOM from a WRTEN node and a WRTBUFENCORE node,responsive to the command signal COM indicative of the write command.The CWL shifter 302 may also provide a column address strobe (CAS) writelatency (CWL) signal from the output node of FFCWL 307.

The core command circuit 30 may include a latch 303 that may receive thelatency sum signal (CWL−1+0) responsive to the internal clock signalfrom the CLK node of the core command circuit 30. An AND circuit 304 mayreceive an output signal from the latch 303 and the internal clocksignal from the CLK node of the core command circuit 30 and may furtherprovide an output signal that is the WRTCLKCORE signal on a WRTCLK0node. The WRTCLKCORE signal may be a cyclic signal having the same cycleas the internal clock signal CLKINT for three cycles while beingactivated, with a delay equivalent to the CWL cycles relative to thecommand signal COM indicative of the write command, responsive to theinternal clock signal CLKINT and the pulse width of three cycles due tothe latency sum signal (CWL−1+0).

The core command circuit 30 may include another latch 305 that mayreceive the CAS write latency (CWL) signal responsive to the internalclock signal from the CLK node of the core command circuit 30. AnotherAND circuit 306 may receive an output signal from the latch 305 and theinternal clock signal from the CLK node of the core command circuit 30and may further provide an output signal that is the WRTCLK signal on aWRTCLK1 node. The WRTCLK signal may be a cyclic signal having the samecycle as the internal clock signal CLKINT for two cycles while beingactivated, with a delay equivalent to the (CWL+1) cycles relative to thecommand signal COM indicative of the write command, responsive to theinternal clock signal CLKINT and the pulse width of two cycles due tothe CAS write latency (CWL) signal.

FIG. 7A is a block diagram of a core write FIFO circuit 36 in the corechip 3 of FIG. 2A, in accordance with an embodiment of the presentdisclosure. FIG. 7B is a timing diagram of signals in the core writeFIFO circuit 36, in accordance with an embodiment of the presentdisclosure.

The core write FIFO circuit 36 may include a pointer circuit (IN) 70 aand a pointer circuit (OUT) 70 b. FIG. 7C is a block diagram of apointer circuit 70 (e.g., the pointer circuit 70 a, the pointer circuit70 a) in the core write FIFO circuit 36, in accordance with anembodiment of the present disclosure. For example, the pointer circuit70 may include a plurality of flip-flop circuits 77 a to 77 d in acascade connection. The pointer circuit 70 may receive a clock signalCLK at a clock node CLK, and provide the clock signal CLK to clock nodesof the plurality of flip-flop circuits 77 a to 77 d. An output node ofeach flip-flop circuit of the plurality of flip-flop circuits 77 a to 77c may be coupled to an input node of a flip-flop circuit in a next stageof the plurality of flip-flop circuits 77 b to 77 d, respectively, inthe cascade connection. In a reset operation, for example, the flip-flopcircuit 77 a may provide an active pointer signal (Ptr=0) at a logichigh level when a pointer count Ptr is zero, responsive to an activereset signal which is provided to a set node (SN) of the flip-flopcircuit 77 a. Simultaneously, in the reset operation, for example, theflip-flop circuits 77 b to 77 d may provide inactive pointer signals(Ptr=1, Ptr=2, Ptr=3) at a logic low level, responsive to the activereset signal provided to reset nodes (RN) of the flip-flop circuits 77 bto 77 d. Responsive to the clock signal CLK, the active pointer signal(Ptr=0) of the flip-flop circuit 77 a may be provided to an input nodeof the flip-flop circuit 77 b. Since the plurality of flip-flop circuits77 a to 77 d may operate in synchronization with the clock signal CLK,the pointer signals (Ptr=0, Ptr=1, Ptr=2, Ptr=3) may be activated inthis order.

The pointer circuit 70 may be the pointer circuit (IN) 70 a or thepointer circuit (OUT) 70 b. For example, the pointer circuit (IN) 70 amay receive the write data strobe signal WRTCLKTSV, which is originallyfrom the internal write data strobe signal WDQS on the IF chip 2, at aCLK node from an InClk node of the core write FIFO circuit 36. Thepointer circuit 70 a may provide pointer_in signals InPtr_0 (Ptr=0),InPtr_1 (Ptr=1), InPtr_2 (Ptr=2), and InPtr_3 (Ptr=3) in order tocontrol timings of receiving data from the DIN node 341. For example,the pointer circuit (OUT) 70 b may receive the WRTCLKCORE signal at aCLK node from an OutClk node of the core write FIFO circuit 36. Thepointer circuit 70 b may provide pointer_out signals OutPtr_0 (Ptr=0),OutPtr_1 (Ptr=1), OutPtr_2 (Ptr=2), and OutPtr_3 (Ptr=3), in order tocontrol timings of providing the data to the DOUT node.

The core write FIFO circuit 36 may include a clock gate block 71 acoupled to the pointer circuit (IN) 70 a and a clock gate block 71 bcoupled to the pointer circuit (OUT) 70 b. FIG. 7D is a block diagram ofa clock gate block 71 (e.g., the clock gate block 71 a, the clock gateblock 71 b) in the core write FIFO circuit 36, in accordance with anembodiment of the present disclosure. For example, the clock gate block71 may be coupled to the pointer circuit 70. The clock gate block 71 mayinclude a plurality of clock gates 78 that receive the clock signal CLKcommonly provided to the pointer circuit 70. Each clock gate of theplurality of clock gates 78 may receive a corresponding pointer signal.For example, a clock gate 78 may include a latch 79 that may receive thecorresponding pointer signal and the clock signal CLK, and an ANDcircuit 80 that may receive an output signal from the latch 79 and theclock signal CLK. The clock gate 78 may provide a pointer-clock signal.For example, the clock gate 78 that receives the pointer signal (Ptr=1)may provide a pointer-clock signal ClkO[0]. Similarly, the clock gates78 that receive the pointer signals (Ptr=1, Ptr=2, Ptr=3) may providethe pointer-clock signals ClkO[1], ClkO[2], ClkO[3]. Because the pointersignals (Ptr=1, Ptr=1, Ptr=2, Ptr=3) may be activated in this order, thepointer-clock signals ClkO[0], ClkO[1], ClkO[2], ClkO[3] may include apulse signal based on a clock signal responsive to the pointer signals(Ptr=0, Ptr=1, Ptr=2, Ptr=3).

The clock gate block 71 may be the clock gate block 71 a or the clockgate block 71 b. For example, the clock gate block 71 a may providepointer-in-clock signals InClk_0, InClk_1, InClk_2 and InClk_3,responsive to the InClk, and the corresponding pointer_in signalsInPtr_0, InPtr_1, InPtr_2, and InPtr_3, in order to control timings ofreceiving data from the DIN node 341. For example, the clock gate block71 b may provide pointer-out-clock signals OutClk_0, OutClk_1, OutClk_2and OutClk_3, responsive to the OutClk and the corresponding pointer_outsignals OutPtr_0, OutPtr_1, OutPtr_2, and OutPtr_3, in order to controltimings of providing data to the DOUT node.

The core write FIFO circuit 36 may include a plurality of FIFO circuits[0] to [3] 72. The core write FIFO circuit 36 may receive the write datastrobe signal WRTCLKTSV at the InClk_0 to InClk_3 nodes of the pluralityof FIFO circuits [0] to [3] 72, respectively. As described earlier, thewrite data strobe signal WRTCLKTSV may include the first pulse for thedon't care data (X) in the first cycle, the second pulse for the firstand second data (A and B) to be received in the second cycle, and thethird pulse for the third and fourth data (C and D) to be received inthe third cycle. As described earlier, the TSV 34 may provide core data,including the don't care data (X) and the first to forth write data (Ato D), on the RWBSTSV signal to the DIN node 341 of the core write FIFOcircuit 36, with the delay due to the TSV 34 relative to the RWBSTSVsignal, responsive to the RWBSTSV signal. For example, the FIFO circuit[0] 72 may include a plurality of flip-flop circuits 73 a and 73 b in afirst stage and a plurality of flip flop circuits 74 a and 74 b in asecond stage.

The flip-flop circuit 73 a may receive the don't care data (X) and thefirst to forth write data (A to D) at a data input node from the DINnode 341 of the core write FIFO circuit 36, responsive to the InClk_0signal received at a clock node of the flip-flop circuit 73 a. Theflip-flop circuit 73 a may latch the first don't care data (X) with adelay of CWL cycles (e.g., from Time “a” to Time “b” in FIG. 7B) and mayprovide the first don't care data (X) as a W0R[0] signal to a data inputnode of the flip-flop circuit 74 a, responsive to a rising edge of theInClk_0 signal. The flip-flop circuit 74 a may latch the first don'tcare data (X) on the W0R[0] signal and may provide the first don't caredata (X) as a W1R[0] signal to a multiplexer 75, responsive to a risingedge of the OutClk_0 signal received at a clock node of the flip-flopcircuit 74 a.

The flip-flop circuit 73 b may receive the don't care data (X) and thefirst to forth write data (A to D) at a data input node from the DINnode 341 of the core write FIFO circuit 36, responsive to an invertedsignal of the InClk_0 signal received at a clock node of the flip-flopcircuit 73 b. The flip-flop circuit 73 b may latch the second don't caredata (X) and may provide the second don't care data (X) as a W0F[0]signal to a data input node of the flip-flop circuit 74 b, responsive toa rising edge of the inverted InClk_0 signal that corresponds to afalling edge of the InClk_0 signal. The flip-flop circuit 74 b may latchthe second don't care data (X) on the W0F[0] signal with a delay of (CWLand a half) cycles (e.g., from Time “c” to a half cycle after Time “d”in FIG. 7B) and may provide the second don't care data (X) as a W1F[0]signal to the multiplexer 75, responsive to a rising edge of an invertedsignal of the OutClk_0 signal received at a clock node of the flip-flopcircuit 74 b, that corresponds to a falling edge of the OutClk_0 signal.The multiplexer 75 may provide the first don't care data (X) responsiveto the rising edge of the OutClk_0 signal and the second don't care data(X) responsive to the falling edge of the OutClk_0 signal to a buffer76. The buffer 76 may provide the first don't care data (X) and thesecond don't care data (X), responsive to the pointer_out signalOutPtr_0 from the pointer circuit 70 b.

Similarly, the FIFO circuit [1] 72 may receive the don't care data (X)and the first to forth write data (A to D), responsive to the InClk_1signal, and provide the first write data (A) and the second write data(B), responsive to a rising edge and a falling edge of the OutClk_1signal, respectively (e.g., from Time “e” and a half cycle after Time“e” in FIG. 7B). The FIFO circuit [2]72 may receive the don't care data(X) and the first to forth write data (A to D), responsive to theInClk_2 signal, and provide the third write data (C) and the fourthwrite data (D), responsive to a rising edge and a falling edge of theOutClk_2 signal, respectively. Thus, the DOUT node of the core writeFIFO circuit 36 may provide the don't care data (X) and the first toforth write data (A to D) as shown in FIG. 2B and FIG. 7D to the buffer38.

It will be understood by those skilled in the art that the IF read FIFOcircuit 28 may have the similar structure as the core write FIFO circuit36, including two stages of a plurality of flip flop circuits, one stagefor receiving data and the other stage for providing the data. Forexample, the IF read FIFO circuit 28 may receive data from one of thecore chips 3, responsive, in part, to an internal clock signal of eitherIF chip 2 or the one of the core chips 3. The IF read FIFO circuit 28may provide the data to the memory controller 1, while the IF commandcircuit 20 may provide a clock signal and a read data strobe signalsignaling timings to read the data to the memory controller 1 and the IFread FIFO circuit 28 (not shown).

Logic levels of signals used in the embodiments described the above aremerely examples. However, in other embodiments, combinations of thelogic levels of signals other than those specifically described in thepresent disclosure may be used without departing from the scope of thepresent disclosure.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the inventions extend beyond the specificallydisclosed embodiments to other alternative embodiments and/or uses ofthe inventions and obvious modifications and equivalents thereof. Inaddition, other modifications which are within the scope of thisinvention will be readily apparent to those of skill in the art based onthis disclosure. It is also contemplated that various combination orsub-combination of the specific features and aspects of the embodimentsmay be made and still fall within the scope of the inventions. It shouldbe understood that various features and aspects of the disclosedembodiments can be combined with or substituted for one another in orderto form varying mode of the disclosed invention. Thus, it is intendedthat the scope of at least some of the present invention hereindisclosed should not be limited by the particular disclosed embodimentsdescribed above.

What is claimed is:
 1. An apparatus comprising: first and secondsemiconductor chips respectively comprising an interface chip and a corechip that are stacked with each other via a plurality of throughsubstrate vias (TSVs) provided in at least one of the first and secondsemiconductor chips; wherein the first semiconductor chip comprisesfirst and second data terminals and a first buffer circuit in theinterface chip, the first buffer circuit including at least one firstflip flop circuit coupled between the first and second terminals,wherein the second semiconductor chip comprises a second buffer circuitin the core chip including: a plurality of serially coupled second flipflop circuits coupled in series; and an input node coupled to the seconddata terminal via at least one of the plurality of TSVs, and wherein thefirst buffer circuit in the interface chip is smaller in a number offlip flop circuits than the second buffer circuit in the core chip. 2.The apparatus of claim 1, wherein the first flip flop circuit isconfigured to latch data on the first data terminal and furtherconfigured to provide a latched data to the second data terminalresponsive to a data strobe signal.
 3. An apparatus comprising: firstand second semiconductor chips that are stacked with each other via aplurality of through substrate vias (TSVs) provided in at least one ofthe first and second semiconductor chips; wherein the firstsemiconductor chip comprises first and second data terminals and a firstbuffer circuit, the first buffer circuit including at least one firstflip flop circuit coupled between the first and second terminals,wherein the second semiconductor chip comprises a second buffer circuitincluding: a plurality of serially coupled second flip flop circuitscoupled in series; and an input node coupled to the second data terminalvia at least one of the plurality of TSVs, and wherein the first buffercircuit is smaller in a number of flip flop circuits than the secondbuffer circuit, wherein the first flip flop circuit is configured tolatch data on the first data terminal and further configured to providea latched data to the second data terminal responsive to a data strobesignal, wherein the plurality of second flip flop circuits comprises athird flip flop circuit coupled to the third data terminal and a fourthflip flop circuit coupled to the third flip flop circuit, wherein thethird flip flop circuit is configured to latch the latched data from thethird data terminal and further configured to provide the latched dataresponsive to the data strobe signal, and wherein the fourth flip flopcircuit is configured to latch the latched data from the third flip flopcircuit and further configured to provide the latched data responsive toa first control signal different from the data strobe signal.
 4. Anapparatus comprising: first and second semiconductor chips that arestacked with each other via a plurality of through substrate vias (TSVs)provided in at least one of the first and second semiconductor chips;wherein the first semiconductor chip comprises first and second dataterminals and a first buffer circuit, the first buffer circuit includingat least one first flip flop circuit coupled between the first andsecond terminals, wherein the second semiconductor chip comprises asecond buffer circuit including: a plurality of serially coupled secondflip flop circuits coupled in series; and an input node coupled to thesecond data terminal via at least one of the plurality of TSVs, andwherein the first buffer circuit is smaller in a number of flip flopcircuits than the second buffer circuit, wherein the first semiconductorchip further comprises a third buffer circuit coupled between the firstdata terminal and the second data terminal, the third buffer circuitincluding a plurality of third flip flop circuits coupled in series. 5.The apparatus of claim 1, wherein the first semiconductor chip furthercomprises: a driver coupled between the first buffer circuit and thesecond data terminal and configured to be activated responsive, at leastin part, to a second control signal, and a width expanding circuitconfigured to provide the second control signal responsive, at least inpart, to the data strobe signal.
 6. An apparatus comprising: a firstsemiconductor chip comprising a first write buffer circuit configured totransmit data from a set of data terminals to a set of output terminals,responsive at least to an active control signal; a second semiconductorchip stacked with the first semiconductor chip via a plurality ofthrough-substrate vias (TSVs) and configured to receive the datatransmitted from the first semiconductor chip to provide output data;wherein the first semiconductor chip further comprises: a data strobesignal receiver coupled to the first write buffer circuit of the firstsemiconductor chip and configured to receive a data strobe signal toprovide an internal data strobe signal; and a width expander circuitcoupled to the data strobe signal receiver to receive the internal datastrobe signal to provide the control signal.
 7. The apparatus of claim6, wherein the first semiconductor chip further comprises a firstcommand circuit configured to provide an enable signal to control thedata strobe signal receiver of the first semiconductor chip, responsiveat least to a clock signal.
 8. The apparatus of claim 7, wherein thefirst command circuit comprises a latency shifter configured to providethe enable signal based at least on the clock signal.
 9. The apparatusof claim 8, wherein the latency shifter comprises a plurality offlip-flop circuits serially coupled and configured to propagate acommand signal through each of the plurality of flip-flop circuits,wherein the enable signal is provided based on a combination of outputsignals of the plurality of flip-flop circuits.
 10. The apparatus ofclaim 6, wherein the first semiconductor chip and the secondsemiconductor chip are configured to transfer the internal data strobesignal from the first semiconductor chip to the second semiconductorchip via a TSV.
 11. The apparatus of claim 6, wherein the firstsemiconductor chip further comprises a data buffer coupled to the firstwrite buffer circuit and configured to provide a delayed data based ondata received from a data input terminal.
 12. The apparatus of claim 11,wherein the expander circuit comprises one or more delay circuitsserially coupled and configured to propagate the internal data strobesignal to provide the control signal.
 13. The apparatus of claim 6,wherein the first semiconductor chip further comprises a first readcircuit configured to read data from the second semiconductor chip toprovide the read data to the set of data terminals responsive at leastto a read command and an inactive control signal.
 14. An apparatuscomprising: first semiconductor chip comprising: a data strobe signalreceiver configured to receive a data strobe signal to provide aninternal data strobe signal; and a first write circuit coupled to thedata strobe signal receiver and configured to receive input data at aninput terminal and provide first output data, responsive at least to theinternal data strobe signal; and a second semiconductor chip stackedwith the first semiconductor chip via a plurality of through-substratevias (TSVs) and configured to receive the first output data from thefirst semiconductor chip to provide second output data at a set ofoutput terminals, wherein the second semiconductor chip comprises: asecond write circuit configured to receive the first output data fromthe first semiconductor chip to provide the second output dataresponsive at least to a first control signal; and a command circuitcomprising a shifter configured to receive a command signal from thefirst semiconductor chip to provide the first control signal, whereinthe first control signal is at a first delay from the command signal.15. The apparatus of claim 14, wherein the command circuit furthercomprises a command decoder coupled to the shifter and configured todecode the command signal to provide a decoded command signal to theshifter.
 16. An apparatus comprising: first semiconductor chipcomprising: a data strobe signal receiver configured to receive a datastrobe signal to provide an internal data strobe signal; and a firstwrite circuit coupled to the data strobe signal receiver and configuredto receive input data at an input terminal and provide first outputdata, responsive at least to the internal data strobe signal; and asecond semiconductor chip stacked with the first semiconductor chip viaa plurality of through-substrate vias (TSVs) and configured to receivethe first output data from the first semiconductor chip to providesecond output data at a set of output terminals, wherein the secondsemiconductor chip comprises: a second write circuit configured toreceive the first output data from the first semiconductor chip toprovide the second output data responsive at least to a first controlsignal; and a command circuit comprising a shifter configured to receivea command signal from the first semiconductor chip to provide the firstcontrol signal, wherein the first control signal is at a first delayfrom the command signal, wherein the command circuit further comprises acommand decoder coupled to the shifter and configured to decode thecommand signal to provide a decoded command signal to the shifter,wherein the first write circuit comprises first flip-flop circuit andsecond flip-flop circuit, the first and second flip-flop circuitscoupled to the input terminal and configured to provide first data ofthe first output data at a rising edge of the internal data strobesignal and second data of the first output data at a falling edge of theinternal data strobe signal, the rising edge and the falling edge are inan active clock cycle of the internal data strobe signal, wherein theshifter comprises a plurality of flip-flops serially coupled topropagate the decoded command signal to provide the first control signalat output of a last flip-flop circuit of the plurality of flip-flopcircuits.
 17. An apparatus of comprising: first semiconductor chipcomprising: a data strobe signal receiver configured to receive a datastrobe signal to provide an internal data strobe signal; and a firstwrite circuit coupled to the data strobe signal receiver and configuredto receive input data at an input terminal and provide first outputdata, responsive at least to the internal data strobe signal; and asecond semiconductor chip stacked with the first semiconductor chip viaa plurality of through-substrate vias (TSVs) and configured to receivethe first output data from the first semiconductor chip to providesecond output data at a set of output terminals, wherein the secondsemiconductor chip comprises: a second write circuit configured toreceive the first output data from the first semiconductor chip toprovide the second output data responsive at least to a first controlsignal; and a command circuit comprising a shifter configured to receivea command signal from the first semiconductor chip to provide the firstcontrol signal, wherein the first control signal is at a first delayfrom the command signal, wherein the first write circuit comprises firstflip-flop circuit and second flip-flop circuit, the first and secondflip-flop circuits coupled to the input teiniinal and configured toprovide first data of the first output data at a rising edge of theinternal data strobe signal and second data of the first output data ata falling edge of the internal data strobe signal, the rising edge andthe falling edge are in an active clock cycle of the internal datastrobe signal, and wherein the second write circuit is furtherconfigured to provide the second output data responsive at least to asecond control signal provided by the command circuit, wherein thesecond control signal is at a second delay from the command signal, thesecond delay is less than the first delay.
 18. An apparatus comprising:first semiconductor chip comprising: a data strobe signal receiverconfigured to receive a data strobe signal to provide an internal datastrobe signal; and a first write circuit coupled to the data strobesignal receiver and configured to receive input data at an inputterminal and provide first output data, responsive at least to theinternal data strobe signal; and a second semiconductor chip stackedwith the first semiconductor chip via a plurality of through-substratevias (TSVs) and configured to receive the first output data from thefirst semiconductor chip to provide second output data at a set ofoutput terminals, wherein the second semiconductor chip comprises: asecond write circuit configured to receive the first output data fromthe first semiconductor chip to provide the second output dataresponsive at least to a first control signal; and a command circuitcomprising a shifter configured to receive a command signal from thefirst semiconductor chip to provide the first control signal, whereinthe first control signal is at a first delay from the command signal,wherein the first write circuit comprises first flip-flop circuit andsecond flip-flop circuit, the first and second flip-flop circuitscoupled to the input terminal and configured to provide first data ofthe first output data at a rising edge of the internal data strobesignal and second data of the first output data at a falling edge of theinternal data strobe signal, the rising edge and the falling edge are inan active clock cycle of the internal data strobe signal, and whereinthe second write circuit comprises: a first pointer circuit configuredto provide a plurality of first internal clocks; and a second pointercircuit configured to provide a plurality of second internal clocks. 19.The apparatus of claim 18, wherein the second write circuit furthercomprises: a plurality of first stage flip-flop circuits coupled to arespective first internal clock of the plurality of first internalclocks and configured to latch data at a rising edge and a succeedingfalling edge of the respective first internal clock; and a plurality ofsecond stage flip-flip circuits coupled to the plurality of first stageflip-flop circuits and a respective second internal clock of theplurality of second internal clocks, the plurality of second stageflip-flop circuits are configured to latch data at a rising edge and asucceeding falling edge of the respective second internal clock.
 20. Theapparatus of claim 1, wherein the first buffer circuit and the secondbuffer circuit are each a write buffer circuit.